Module Pygame - "FadeOut" text

[Askari]

(Help for Pygame module)

Hi, 
   How I can make a "fadeout text"(alpha at 255,254,253...0) on a surface 
and my surface's background must be transparatly?
Note : I can do  a fadeout but with a background on the surface's text but 
I wan't a tranparently background. 


Example (don't work) : 
"""
text = self.maFont12.render("Blablablabla", 1, (0,255,0))  #No Background
                                                        #Foreground green
text.set_alpha( i )  
app.blit( text ,(10,10))
"""

where "self.maFont12" is a font objet and "app" my destination surface and 
"i" the alpha number (255,254,253,... 0)


Askari